The age of Machir's Sons

Question

I am trying to understand a comment written in the Stone Edition Chuash (page 288) on Bereishit 50:23. On the statement that Yosef was alive to have his great-great grandchildren through Ephraim on his knees, and the sons of Machir, his grandson through Menashe, also on his knees, the commentary reads,

"The point has been made that Machir's sons were contemporaries of Moses (Numbers 26:29), and they were among the fourth generation that God had promised to liberate from Egypt (15:16). When they were children, they had seen Joseph, the greatest of his generation, and they would live to enter Eretz Yisrael."

According to the Jewish Timeline Encyclopedia, Yosef died in 2309, the slavery began in 2332, and the Exodus was in 2448. The slavery was then 116 years long and Machir and his sons were alive for at least 139 years (the youngest, assuming they were born on the day Yosef died) and probably older than that to have been able to spend any appreciable time on Yosef's knees. Ignoring the incredible age to which they lived (minimum 139 years old when even Levi died at 137) how could they enter the land of Israel -- wouldn't they have been condemned to die in the desert as they were older than 20 years old?

Answer 1

It's possible that this comment is based on the midrash in Bamidbar Rabbah 14:7 which says:

"...הֲרֵי שְׁלשָׁה כְּנֶגֶד שְׁלשָׁה דוֹרוֹת שֶׁרָאָה יוֹסֵף מִן מְנַשֶּׁה שֶׁנָּטְלוּ חֵלֶק בָּאָרֶץ, שֶׁנֶּאֱמַר (בראשית נ, כג): גַּם בְּנֵי מָכִיר בֶּן מְנַשֶּׁה יֻלְדוּ עַל בִּרְכֵּי יוֹסֵף, וְכֵן הוּא אוֹמֵר (במדבר כו, כט ל): בְּנֵי מְנַשֶּׁה לְמָכִיר מִשְׁפַּחַת הַמָּכִירִי וּמָכִיר הוֹלִיד אֶת גִּלְעָד וגו' אֵלֶּה בְּנֵי גִּלְעָד אִיעֶזֶר וגו', מָכִיר וְגִלְעָד וְאִיעֶזֶר, הֲרֵי שְׁלשָׁה דוֹרוֹת שֶׁהָיוּ בָּתֵּי אָבוֹת שֶׁנִּקְרְאוּ עַל שֵׁם יוֹסֵף, כִּי מְנַשֶּׁה עַל שֵׁם יַעֲקֹב נִקְרָא, כְּמָה דְתֵימָא (בראשית מח, ה): וְעַתָּה שְׁנֵי בָנֶיךָ הַנּוֹלָדִים לְךָ בְּאֶרֶץ מִצְרַיִם עַד בֹּאִי אֵלֶיךָ מִצְרַיְמָה לִי הֵם, וְהָרְבִיעִי זֶה הָיָה יָאִיר בֶּן מְנַשֶּׁה שֶׁנָּטַל חֵלֶק בָּאָרֶץ, כְּמָה דְתֵימָא (במדבר לב, מא): וְיָאִיר בֶּן מְנַשֶּׁה הָלַךְ וַיִלְכֹּד אֶת חַוֹּתֵיהֶם וַיִּקְרָא אֶתְהֶן חַוֹּת יָאִיר..."

Translation: So [we] have three against the three generations that Yosef saw from Menasheh that received portions in the land, as it says: "the children of Machir son of Manasseh were likewise born upon Joseph’s knees" and it is also said: "Descendants of Manasseh: Of Machir, the clan of the Machirites.—Machir begot Gilead.—Of Gilead, the clan of the Gileadites. These were the descendants of Gilead: [Of] Iezer etc" Machir and Gilad and Iezer, therefore three generations which were clans that were named after Yosef, for Menasheh was named after Yaakov, as it is written: "Now, your two sons, who were born to you in the land of Egypt before I came to you in Egypt, shall be mine" and the fourth was Yair ben Menasheh who took a portion in the land, as it is written: "Jair son of Manasseh went and captured their villages, which he renamed Havvoth-jair"..."

In which case, it seems that the idea is that symbolically Machir and his son(s) entered Yisrael, as there were clans (בתי אב) named after each of them.